Effects of fiber and virginiamycin on nutrient absorption, nutrient retention and rate of passage in growing swine.

Three balance trials, each involving 12 crossbred gilts averaging 35.2 kg body weight, were conducted to determine the effects of dietary fiber and virginiamycin on nutrient digestibility, mineral absorption and retention, and digesta rate of passage (RP). Two levels of fiber (13.5 and 20.2% neutral detergent fiber) and two levels of virginiamycin (0 and 11 ppm) were used in a 2 X 2 factorial arrangement of treatments. All diets were isonitrogenous and isocaloric. The RP was determined by observing the time required for a change in feces color after the addition of .5% chromic oxide to the diet. The high fiber diet had a faster (P less than .01) RP, which was associated with depressions (P less than .001) in the digestibility of dry matter (DM), energy (E), cell contents, neutral detergent fiber (NDF), acid detergent fiber (ADF), hemicellulose (HC), cellulose, permanganate lignin and ash. Virginiamycin supplementation slowed (P less than .004) the RP of both low and high fiber diets, but improved (P less than .05) the DM, E, NDF, ADF, HC and cellulose digestibility of the high fiber diet only. Fiber increased (P less than .06) fecal N excretion, whereas virginiamycin supplementation decreased (P less than .08) fecal N excretion. The addition of virginiamycin improved the absorption and retention of P, Ca, Mg, Cu, Fe, Zn and Mn when added to the high fiber diet, but had little or no effect when added to the low fiber diet even though absorption and retention values for most minerals were similar or slightly higher for the unsupplemented high fiber diet compared with the unsupplemented low fiber diet.(ABSTRACT TRUNCATED AT 250 WORDS)